In general, various portable terminals such as a mobile phone and a PDA (Personal Digital Assistant) are equipped with a power receiving device such as a battery pack charged with a power to supply an operation power. The power receiving device is charged with a power from an external charging device and supplies the power to a portable terminal so that the portable terminal can operate.
The power receiving device may include battery cells charged with a power and a charging/discharging circuit for charging the battery cells with power from an external charging device and supplying the charged power to a portable terminal, and the like.
As a type of connecting the charging device and the power receiving device, there has been known a terminal connection type that directly connects a power output terminal of a charging device, which receives a utility AC power and outputs a power of a voltage and a current corresponding to the power receiving device, with a power input terminal of the power receiving device through a cable.
However, according to the terminal connection type, there is a potential difference between the terminal of the charging device and the terminal of the power receiving devices, so instantaneous discharge is generated when the terminal of the charging device and the terminal of the power receiving device are brought in contact with each other or separated from each other.
The instantaneous discharge wears the terminal of the charging device and the terminal of the power receiving device, and when dirt is accumulated on the terminal of the charging device and the terminal of the power receiving device, heat is generated from the dirt and may cause a safety accident such as a fire.
The power stored in the battery cells of the power receiving device is naturally discharged to the outside through the terminal of the power receiving device due to humidity etc., so there is a problem in that the lifespan and performance of the power receiving device are decreased.
Recently, in order to solve the various problems with the terminal connection type, a wireless power receiving device that charges battery cells by receiving a wireless power signal transmitted from a wireless power transmitting device has been proposed (see Korean Patent Application Publication No. 10-2012-0128114).
The wireless power receiving device is, for example, connected with the wireless power transmitting device in an electromagnetic induction type, receives a wireless power signal wirelessly transmitted from the wireless power transmitting device, and charges battery cells with a received power.
There have been many efforts for allowing the wireless power receiving device to wirelessly receive a power stably and with high efficiency and charge battery cells.
The wireless power receiving device rectifies a wireless power signal received from the wireless power transmitting device with a rectifier to convert it to a DC power and the voltage level of the DC power is converted to a voltage level corresponding to the battery cells by a DC/DC converter and then the battery cells are charged with the power.
However, converting the voltage level of the DC power with the DC/DC converter generates a large amount of heat while the DC/DC converter converts the voltage level of DC power, so power consumption increases and there is a need for a specific heat discharge unit for discharging the heat generated from the DC/DC converter.
Further, since the heat discharge unit is mounted on a circuit board, the circuit board increases in size.